Another reason we have launch windows is to line up with planets. Sometimes, spacecraft get close to a planet in a gravitational slingshot, where they steal a little bit of the planet’s orbital motion to get a boost.
But in the case of the Hail Mary, this was an interstellar trip, so there was no need to align with anything. The concept of a launch window doesn’t make sense. It was just shorthand in the movie for the fact that it would take too long to train someone else. I think it was misleading to use those terms, but I do understand the need to communicate something to the audience efficiently.
Astrophage
Let’s take a look at the interstellar troublemakers in Project Hail Mary, astrophage.
They are microscopic organisms, colonizing the Sun and slowly dimming it. They need the carbon dioxide in Venus’s atmosphere to reproduce, so they travel there, but then they head back to the Sun to gain energy. To travel, they emit infrared radiation at a wavelength of 25.984 microns, which they call the “Petrova wavelength”. Even while on the Sun, astrophages maintain an internal temperature of 96.415 degrees C. The idea is that they turn the extra energy from the Sun into mass, via E=mc2. Then, when they need to emit energy to move, they turn mass back into energy.
How can you convert energy into mass, and vice versa? It happens all the time in nature. When matter and antimatter collide, they annihilate each other and produce energy. But the reverse process can also happen, when two high-energy bits of light, photons, come together, their energy gets turned into matter in a process called pair production. It is a pair because you have to make a particle and its antiparticle, like an electron and a positron, which is a positively charged electron. The amount of energy in the photons determines the mass of particles that you can make.
Ryan Gosling stars as Ryland Grace in PROJECT HAIL MARY, from Amazon MGM Studios.
Photo credit: Jonathan Olley
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“So Andy had to invent a way to trap neutrinos.”
The key to the inner workings of an astrophage is neutrinos. Neutrinos are tiny particles with really low mass. They can pass through just about anything without interacting. In fact, about 100 trillion neutrinos pass through your body every second! They’re produced in nuclear reactions in the core of the sun. While light produced there is scattered so many times it takes about a hundred thousand years to work its way to the surface, neutrinos stream out immediately, because nothing can stop them.
So Andy had to invent a way to trap neutrinos.
The math actually works out — even though we don’t know their exact mass, it is plausible that annihilating neutrinos would produce radiation at 25.984 microns. In the book, it takes this magic temperature of 96.415 degrees C to reach the energy threshold to smash together hydrogen to make neutrinos.
Colliding two protons in real life at high enough energy fuses them together, and it’s how the sun makes energy. Two protons come together to make deuterium, which is a neutron and a proton stuck together, along with a neutrino and a positron. The idea in Project Hail Mary is that somehow, at lower energies, they do something different. Sure, this violates what we know from particle physics, but hey, in science fiction, you get to posit a miracle to set your plot in motion. So while Andy Weir made up this form of neutrino production, I love the fact that after that, the math all works out.
Xenonite
Rocky’s favorite material is something called Xenonite. That’s a fictional compound, of course. Xenon is a noble gas, and those aren’t really supposed to make chemical bonds easily. Andy Weir told me he specifically chose it to confuse scientists and show that the Eridians are way ahead of us in material science. And the choice isn’t complete speculation. Xenon can bond with Fluorine to make a solid. Under some conditions, it can even bond with gold, forming the wonderfully named Tetraxenonogold! A noble gas and a noble metal coming together, now that’s some weird chemistry.
Breediing Nitrogen Resistant Taumoeba
In Project Hail Mary, astrophages are killed by Taumoeba, a life form native to the planet Adrian around the star Tau Ceti. But the problem is, Taumoeba dies when exposed to nitrogen. Since Venus has nitrogen, this would prevent us from using them to stop the Sun’s cooling. So Grace and Rocky have to breed nitrogen-resistant Taumoeba in tanks they made from Xenonite, by exposing some to tiny amounts of nitrogen, collecting the survivors, and repeating this process over and over.
We’ve done this kind of thing on Earth. As the book points out, antibiotics lose potency over time because bacteria become resistant to them. In fact, you can see this dramatically illustrated with a MEGA plate. These are giant petri dishes with zones of increasing levels of antibiotics. As bacteria come to the edge of one zone, they stall for a while until a mutation develops. Then that zone is filled, and the process repeats. In just 11 days, they can develop a thousandfold resistance to antibiotics. But it gets even crazier. Scientists have effectively created new versions of E. Coli in the laboratory with selective breeding, which have superpowers that natural forms don’t, like the ability to eat citrate, which is related to citric acid.
